c.md

layout	title
../../layouts/CheatSheet.astro	C Cheatsheet

Synopsis

C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis M. Ritchie at the Bell Telephone Laboratories to develop the UNIX operating system. C is the most widely used computer language. It keeps fluctuating at number one scale of popularity along with Java programming language, which is also equally popular and most widely used among modern software programmers.

Data Types

Data Type	Description	Size
char	Character	1 byte
int	Integer	2 or 4 bytes
float	Floating point	4 bytes
double	Floating point	8 bytes
void	Void	1 byte

Operators

Operator	Description	Example
+	Addition	a + b
-	Subtraction	a - b
*	Multiplication	a * b
/	Division	a / b
%	Modulus	a % b
++	Increment	a++
--	Decrement	a--
=	Assignment	a = b
==	Equal to	a == b
!=	Not equal to	a != b
>	Greater than	a > b
<	Less than	a < b

Control Flow

Statement	Description
if	Executes a block of code if a condition is true
if...else	Executes a block of code if a condition is true, otherwise executes another block of code
switch	Executes a block of code depending on the value of a variable
while	Executes a block of code while a condition is true
do...while	Executes a block of code while a condition is true, and then executes the code once more

Functions

Function	Description
printf()	Prints formatted output
scanf()	Reads formatted input
strlen()	Returns the length of a string
strcpy()	Copies a string
strcat()	Concatenates two strings
strcmp()	Compares two strings
strrev()	Reverses a string
strlwr()	Converts a string to lowercase
strupr()	Converts a string to uppercase
getch()	Reads a character from the keyboard
getche()	Reads a character from the keyboard and displays it on the screen
putch()	Writes a character to the screen

Arrays

Function	Description
int a[10];	Declares an array of 10 integers
int a[5] = {1, 2, 3, 4, 5};	Declares an array of 5 integers and initializes it
int a[] = {1, 2, 3, 4, 5};	Declares an array of 5 integers and initializes it
int a[5] = {1, 2, 3};	Declares an array of 5 integers and initializes the first 3 elements

Pointers

Function	Description
int *p;	Declares a pointer to an integer
int *p = &a;	Declares a pointer to an integer and initializes it to the address of a
int *p = a;	Declares a pointer to an integer and initializes it to the address of a
int *p = NULL;	Declares a pointer to an integer and initializes it to NULL
*p = 10;	Assigns the value 10 to the variable pointed to by p
p++;	Increments the pointer p by 1
p--;	Decrements the pointer p by 1

Structures

Function	Description
struct student { int rollno; char name[20]; };	Declares a structure named student
struct student s1;	Declares a variable s1 of type student
struct student s1 = {1, "John"};	Declares a variable s1 of type student and initializes it
struct student s1 = {.name = "John", .rollno = 1};	Declares a variable s1 of type student and initializes it
struct student s1; s1.rollno = 1; strcpy(s1.name, "John");	Declares a variable s1 of type student and initializes it

Unions

Function	Description
union student { int rollno; char name[20]; };	Declares a union named student
union student s1;	Declares a variable s1 of type student
union student s1 = {1};	Declares a variable s1 of type student and initializes it

Enumerations

Function	Description
enum week { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };	Declares an enumeration named week
enum week day;	Declares a variable day of type week
enum week day = Tuesday;	Declares a variable day of type week and initializes it

Bit Fields

Function	Description
struct { unsigned int widthValidated; unsigned int heightValidated; } status1;	Declares a structure with two bit fields
struct { unsigned int widthValidated : 1; unsigned int heightValidated : 1; } status1;	Declares a structure with two bit fields

Typedef

Function	Description
typedef int INTEGER;	Declares a new type named INTEGER
typedef struct { int rollno; char name[20]; } STUDENT;	Declares a new type named STUDENT

Preprocessor Directives

Directive	Description
#include	Includes a header file
#define	Defines a macro
#undef	Undefines a macro
#ifdef	Checks if a macro is defined
#ifndef	Checks if a macro is not defined
#if	Checks if a condition is true
#else	Executes a block of code if a condition is false
#elif	Checks if a condition is true
#endif	Ends an if statement
#error	Generates an error
#pragma	Generates a compiler directive

Input/Output

Function	Description
printf()	Prints formatted output
scanf()	Reads formatted input
fprintf()	Prints formatted output to a file
fscanf()	Reads formatted input from a file
sprintf()	Prints formatted output to a string
sscanf()	Reads formatted input from a string
puts()	Prints a string
gets()	Reads a string
putchar()	Prints a character
getchar()	Reads a character

String Functions

Function	Description
strlen()	Returns the length of a string
strcpy()	Copies a string
strcat()	Concatenates two strings
strcmp()	Compares two strings
strrev()	Reverses a string
strlwr()	Converts a string to lowercase

Math Functions

Function	Description
abs()	Returns the absolute value of an integer
fabs()	Returns the absolute value of a floating point number
ceil()	Returns the smallest integer greater than or equal to a floating point number
floor()	Returns the largest integer less than or equal to a floating point number
sqrt()	Returns the square root of a number
pow()	Returns the value of a number raised to a power
exp()	Returns the value of e raised to a power

Time Functions

Function	Description
time()	Returns the current time
clock()	Returns the number of clock ticks elapsed since the program was launched
difftime()	Returns the number of seconds between two times
mktime()	Converts a time structure to a time value
asctime()	Converts a time structure to a string
ctime()	Converts a time value to a string
gmtime()	Converts a time value to a time structure in UTC
localtime()	Converts a time value to a time structure in the local time zone

File Functions

Function	Description
fopen()	Opens a file
fclose()	Closes a file
fgetc()	Reads a character from a file
fputc()	Writes a character to a file
fgets()	Reads a string from a file
fputs()	Writes a string to a file
fread()	Reads data from a file
fwrite()	Writes data to a file
fseek()	Sets the position indicator associated with a file
ftell()	Returns the current value of the position indicator of a file
rewind()	Sets the position indicator associated with a file to the beginning of the file
remove()	Deletes a file
rename()	Renames a file
tmpfile()	Creates a temporary file
tmpnam()	Generates a temporary file name